Complete user datagram protocol (CUDP) for wireless multimedia packet networks using improved packet level forward error correction (FEC) coding

ABSTRACT

A complete User Datagram Protocol (CUDP) is disclosed that reduces packet loss. Channel frame error information is used with a packet level forward error correction (FEC) coding technique to accommodate wireless multimedia traffic. Each packet, as well as the channel frame error information, is forwarded to a given application. The CUDP protocol further assists the FEC decoding process by forwarding the locations of corrupted frames to the FEC decoder. Maximal Distance Separable (MDS) codes can be applied to a group of packets, to achieve additional robustness. An MDS decoder utilizes the frame error information to recognize the erasures within each packet. The error information can be represented as a set of LTU error indicators associated with each packet (for FEC decoders requiring an erasure indicator). The error indicators point to the starting and ending location of the erroneous data. The error information can also be represented as a reformatted packet (for FEC decoders Recognizing Erasures). The frame (LTU) error information from the lower layers is incorporated in the packet payload. An FEC encoder is also disclosed that encodes multimedia packets utilizing a packet-coding scheme, such as a Vertical Packet Coding (VPC) scheme or a Long Vertical Packet Coding (LVPC) scheme.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 09/668,242, filed on Sep. 22, 2000 and is related to U.S.patent application Ser. No. 09/668,243 entitled “Radio Link Protocol(RLP)/Point-to-Point Protocol (PPP) Design for Wireless MultimediaPacket Networks that Passes Corrupted Data and Error LocationInformation Among OSI Layers,” assigned to the assignee of the presentinvention and incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to wireless packet networks, andmore particularly, to methods and apparatus for reducing lost orcorrupted packets in such wireless packet networks.

BACKGROUND OF THE INVENTION

It is inevitable that future wireless services will support InternetProtocol (IP)-based multimedia applications. For example, current andemerging wireless networks allow (i) a user to download information fromthe Internet using a wireless communication device, (ii)Internet-to-mobile or mobile-to-mobile videoconferences, (iii) streamingof video or audio information (or both) from the Internet to a wirelesscommunication device, and (iv) electronic-commerce applications. Ingeneral, the multimedia services can be classified into two categories.Real-time services generally have delay constraints but can toleratechannel errors, and include interactive services, such as voice,voice-over-IP, packet video/audio, videoconference applications.Non-real-time services, on the other hand, are generally sensitive tochannel errors but have more relaxed latency requirements, and includeWeb browsing, electronic mail and file transfer protocol (FTP)applications. It is noted, however, that non-real-time services forwireless systems should still provide a reasonable level of latency inorder to be compatible with performance on a wired network, such as theInternet.

The end-to-end path of many wireless multimedia sessions, such as anInternet-to-mobile communication, involves a number of heterogeneousnetwork technologies, with the multimedia packets being sent from anoriginating server, through the Internet and then over one or morewireless packet networks to the mobile destination. Network congestionon the Internet leads to packet loss and degraded quality. Thus, mostInternet-based real-time multimedia services employ the well-known UserDatagram Protocol (UDP) as their transport protocol. Compared to theTransmission Control Protocol (TCP), the UDP protocol has low overheadand no retransmission delay, which makes it attractive to delaysensitive applications.

A UDP packet typically includes a header, containing source anddestination address information, as well as a payload (the actualapplication data). The UDP protocol employs a cyclic redundancy check(CRC) to verify the integrity of packets, in a known manner. The UDPprotocol can detect any error in the packet header or payload anddiscard the packet if an error is detected. Packet transmission based onthe UDP protocol on the Internet is a “best efforts” protocol, wherenetwork congestion yields packet loss. When a packet fails to arrivebefore its processing time, the UDP protocol declares the packet aslost. Therefore, at the receiving host, packets are either perfect orcompletely lost.

Wireless packet networks encounter packet losses between a base stationand a mobile receiver as a result of channel errors and networkcongestion. Furthermore, such packet losses can be random or bursty,depending on the environment, rate-of-motion and network loading.Therefore, it has been recognized that use of the UDP protocol in awireless network will cause considerable packet losses, and as a result,poor audio/video quality and increased power consumption. Theinefficiency of the UDP protocol in wireless networks arises from thediscarding of a packet containing only a small portion of corrupteddata. As such, the UDP protocol also discards error-free data within thepacket. Indeed, current and emerging multimedia coding technologies arefocusing on improved error resilience, such that the media decoder cantolerate a certain number of channel errors. Thus, a need exists for arevised UDP protocol that reduces or avoids unnecessary packetdiscarding.

When wireless channels have a fairly high bit error rate, packet-levelforward error correction (FEC) coding techniques, such as thosedescribed in R. Blahut, Theory and Practice of Error Control Codes(Addison-Wesley, 1983), provide an effective way to mitigate channelunreliability and improve media quality. Typically, FEC techniques applyMaximal Distance Separable (MDS) codes, such as Reed-Solomon (RS) codes,across the packets to recover lost packets. Generally, an FEC encodertypically chooses k information packets and generates n−k parity packetsof length n to construct an (n, k) RS code. For IP transmission, thepackets are numbered and are assumed to arrive perfectly or never arriveat all. The missing packets can be detected by the receiver and declaredas erasure packets. An (n, k) RS code can correct (n−k) erasures andthus recover up to (n−k) packet losses.

In a wireless network employing the UDP protocol, an FEC decoder woulduse only the packets that were received perfectly, and lost packets areconsidered erasures. However, the UDP protocol yields high packet lossrates even under low and medium physical layer data losses. Therefore,the (n−k) value employed by the FEC encoder should be sufficiently largeto effectively reduce the packet loss, which implies increased overheadand less efficiency. On the other hand, in a wireless network employingthe UDP Lite protocol, which performs a checksum based on the packetheader, so that only corrupted packet headers result in packet loss, theFEC decoder may receive perfect or corrupted packets, and performs botherror and erasure correction. Since MDS codes provide twice the erasurerecovering capability compared to error correction capability, an (n, k)packet code can recover up to (n−k)/2 erroneous packets within every npackets.

SUMMARY OF THE INVENTION

We have recognized that the above-described shortcomings of the UDPprotocol may be overcome by a revised UDP protocol, referred to hereinas the complete User Datagram Protocol (CUDP), that reduces unnecessarypacket discarding.

More specifically, we have developed the CUDP that includes new packethandling procedures and reduces unnecessary packet discarding. Thedisclosed CUDP protocol utilizes channel frame error informationobtained from the physical and link layers to assist the packet levelerror recovery. In addition, the CUDP supports packet level FEC codingin order to reduce information loss.

The present invention forwards each packet, as well as the channel frameerror information, to a given application. In particular, the disclosedCUDP protocol further assists the packet level FEC decoding process byforwarding the locations of corrupted frames to the FEC decoder. Atransmitter in accordance with the present invention optionally appliesFEC techniques employing Maximal Distance Separable (MDS) codes to agroup of packets, to achieve robustness against packet loss within theInternet and against packet error over wireless channels. At thereceiver, the CUDP protocol forwards the frame error information, aswell as the packet data, to the application layer. An MDS decoderutilizes the frame error information to recognize the erasures withineach packet.

The error information provided to the application layer can berepresented in a number of forms. Upon receiving a packet, the CUDPprotocol only performs a packet header CRC check (and not a payload CRCcheck). In one implementation, a set of logical transmission unit (LTU)error indicators associated with each packet is provided to theapplication layer (for FEC decoders requiring an erasure indicator). Ifthe packet header is valid, the UDP layer forwards the indicator, theLTU size and the packet payload to the FEC decoder. In anotherimplementation, a reformatted packet is provided to the applicationlayer (for FEC decoders Recognizing Erasures). The frame (LTU) errorinformation from the lower layers is incorporated in the packet payload.In this case, if a physical frame is corrupted, the payload within theframe is represented as a set of erasures, which can be recognized bythe FEC decoder. For a valid packet header, the CUDP protocol passes thereformatted packet payload to the upper layers. An FEC encoder is alsodisclosed that encodes multimedia packets utilizing a packet-codingscheme.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional multimedia network environment;

FIG. 2 illustrates a conventional wireless packet network of FIG. 1 infurther detail;

FIG. 3 illustrates a conventional wireless protocol stack and packetstructure in accordance with the present invention;

FIG. 4 illustrates a packet-level forward error correction (FEC) coderin accordance with the present invention; and

FIGS. 5A and 5B illustrate a vertical packet coding (VPC) scheme and along vertical packet coding (LVPC) scheme, respectively, employed by theFEC coder of FIG. 4 in accordance with the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a conventional heterogeneous network environment 100that supports IP-Wireless multimedia communications. As shown in FIG. 1,the end-to-end path of many wireless multimedia sessions, such as anInternet-to-mobile communication, involves a number of heterogeneousnetwork technologies, with the multimedia packets being sent from anoriginating server 105, through the Internet 110 and then over one ormore wireless packet networks 200-n, shown in further detail in FIG. 2,to the mobile destination 140.

UDP and FEC in Wireless Packet Networks

FIG. 3 illustrates a general wireless protocol stack 310 and packetstructure 320. The link layer 330 partitions each single data packetinto multiple units to accomplish physical layer transmission. The unitsize depends on the radio link protocol (RLP), medium access control(MAC) and physical layer (PHY) 335, but is usually much smaller than thepacket size. In 3G wireless systems, for example, each physical layerframe corresponds to a transmission unit, assuming low and medium datarates. To support high data rate services, the MAC layer specifies thatthe RLP layer can subdivide each physical layer frame into smallerlogical frames, referred to as LTUs, each associated with a 16 bit CRC.Typical LTU size ranges from 300-600 bits (40-80 bytes), while IPpackets are typically 600-1500 bytes long.

At the receiver 140, the RLP can specify a limited number ofretransmissions to compensate for LTU losses. The RLP forwards thereceived LTUs to the interface, e.g., Point-to-Point Protocol, toreconstruct the packet. For non-real-time services, PPP forwards thepackets to the TCP layer, where the packet losses after RLPretransmissions can be recovered at the TCP level through packet levelretransmission and congestion control. For real-time services employingUDP, upon receiving a packet from the PPP protocol layer, theconventional UDP layer performs a packet level cyclic redundancy check(CRC) to validate the information within the packet, including both thepacket header and the payload. In this case, any LTU loss would resultin the whole packet being discarded. Mathematically, the packet lossrate (PER) can be approximated as:PER=1−(1−p)^(m) ≈mp (for large m and small p),where m is the number of LTUs per packet and p is the LTU error rate(LER) after retransmission. Therefore, using a conventional UDP in awireless network will yield a considerable amount of packet loss, and asa result, poor video/audio quality and increased power consumption. Theinefficiency of UDP in wireless networks arises from the discarding of apacket containing only a small part of corrupted data. As such, the UDPalso throws out error-free data within the packet. Indeed, applicationscan utilize error-free data to recover corrupted data.

The reliable UDP (RUDP) was proposed to provide reliable ordereddelivery of packets up to a maximum number of retransmissions forvirtual connections. For a more detailed discussion of RUDP, see, T.Bova and T. Krivoruchk, “Reliable UDP Protocol”, Internet Draft, NetworkWorking Group, <draft-ietf-sigtran-reliable-udp-00.txt>, incorporated byreference herein. Generally, the RUDP protocol calculates the CRCchecksum on the packet header alone or the packet header and thepayload. This flexibility makes the RUDP protocol suitable for transporttelecommunication signaling.

Similarly, the UDP Lite protocol was proposed to prevent unnecessarypacket loss at the receiver if channel errors occur only in the packetpayload. For a more detailed discussion of the UDP Lite protocol, see,L. Larzon et al., “Efficient Use of Wireless Bandwidth for MultimediaApplications,” 187-193, MoMuc 99, San Diego (November 1999),incorporated by reference herein. The UDP checksum is constructed basedon the packet header, so that only corrupted packet headers result inpacket loss. The UDP Lite protocol delivers the packet payload to theupper layers, whether the payload is perfect, lost or erroneous.Compared to UDP, UDP lite only performs CRC on the packet header.Therefore, if corrupted, a packet payload will not result in the packetbeing discarded. However, the error location within the packet payloadis unknown to the application, which can improve packet level FECperformance.

When wireless channels have a fairly high bit error rate, packet-levelforward error correction (FEC) coding techniques, such as thosedescribed in R. Blahut, Theory and Practice of Error Control Codes(Addison-Wesley, 1983), provide an effective way to mitigate channelunreliability and improve media quality. These FEC techniques arecurrently being considered by the Internet Engineering Task Force (IETF)for supporting real-time multimedia communications on the Internet andover wireless networks. See, for example, D. Budge et al.,“Media-Independent Error Correction Using RTP,” Internet EngineeringTask Force Internet Draft (May 1997); S. Wenger and G. Côté, “UsingRFC2429 and H.263+ At Low To Medium Bit-Rates For Low-LatencyApplications,” Packet Video '99, New York, N.Y., USA (April 1999); M.Gallant and F. Kossentini, “Robust and Efficient Layered H.263 InternetVideo Based on Rate-Distortion Optimized Joint Source/Channel Coding”,Packet Video '00 (Italy, 2000); S. Wenger and G. Côté, “Test ModelExtension Justification for Internet/H.323 Video Transmission”, DocumentQ15-G-17, ITU Q15, Video Coding Experts Group (February 1999); and J.Rosenberg and H. Schulzrinne, “An RTP Payload Format For Generic ForwardError Correction,” Internet Draft, February 1999, available fromhttp://info.internet.isi.edu:80/in-drafts/files/draft-ietf-avt-fec-05.txt,each incorporated by reference herein.

Complete UDP

As previously indicated, the UDP and UDP Lite protocols do not performwell with packet based FEC. One significant reason is that the UDP andUDP Lite protocols ignore useful channel information from the RLP layer330. The present invention recognizes that such information can beexploited to maximize FEC coding efficiency. However, the currentprotocol design does not support information communications from the RLPlayer 330 to the PPP/IP/UDP layers and above. The present inventionproposes a new system protocol design that allows the exchange ofcertain information in both directions among the layers 310. For a moredetailed discussion of communications between the RLP and PPP layers inthe conventional open system interconnection (OSI) model, see co-pendingU.S. patent application Ser. No. 09/668,243 entitled “Radio LinkProtocol (RLP)/Point-to-Point Protocol (PPP) Design for WirelessMultimedia Packet Networks that Passes Corrupted Data and Error LocationInformation Among OSI Layers,” incorporated by reference above. Arevised UDP protocol, referred to herein as the complete User DatagramProtocol (CUDP), is disclosed that reduces or avoids the discarding ofunnecessary packets by passing the LTU error information as well as thecorrupted packets to the Packet FEC decoder. Depending on theimplementation of the FEC decoder, the error information can berepresented in two forms:

LTU Error Indicator: (For FEC Decoders Requiring Erasure Indicator)

Upon receiving a packet, the UDP protocol only performs a packet headerCRC check (and not a payload CRC check), in a similar manner to the UDPLite protocol. The LTU error information obtained from the lower layersis represented in terms of a set of error indicators that are associatedwith each packet. The error indicators point to the starting and endinglocation of the erroneous data. If the packet header is valid, UDPforwards the indicator, the size of LTU as well as the packet payload tothe FEC decoder.

Reformatted Packet: (For FEC Decoders Recognizing Erasures)

Upon receiving a packet, the UDP protocol performs a packet header CRCcheck. The LTU (referred to herein as “frame”) error information fromthe lower layers is incorporated in the packet payload. In this case, ifa physical frame is corrupted, the payload within the frame isrepresented as a set of erasures, which can be recognized by the FECdecoder. The erasure format depends on the system implementation. Undera valid packet header, UDP passes the reformatted packet payload to theupper layers. The proposed UDP protocol captures all of the availableinformation, i.e., the error-free frames and the location of erroneousframes.

Packet Based FEC Coding Scheme

According to another aspect of the present invention, an FEC codingtechnique is disclosed that uses the available wireless frame errorinformation. Conventional MDS codes were designed for Internetmultimedia applications, where packet loss is congestion related. Forwireless multimedia applications, most packets are partially damaged bychannel errors. Thus, if a conventional UDP protocol was utilized, suchpartially damaged wireless packets would be discarded. Similarly, if aconventional UDP Lite protocol was utilized, such partially damagedwireless packets are forwarded to the application, but the location ofthe error is discarded, thereby leading to information loss.

FIG. 4 illustrates an FEC coder 400 in accordance with the presentinvention that encodes multimedia packets utilizing one of twoillustrative packet-coding schemes, discussed further below inconjunction with FIGS. 5A and 5B. The illustrative FEC encoder 400 codesevery four packets together, and generates three parity checks. Thus, a(7,4) MDS code is employed in the illustrative embodiment. At thewireless physical layer, each packet is segmented into seven frames.

Vertical Packet Coding (VPC) Scheme

The FEC encoder 400 selects k packets of length X units. The proposedsystem encodes multiple packets of the same size together. For real-timeapplications, the packets should have the same or similar delayconstraint, e.g., packets correspond to a single video frame. Thepackets can be of different length. If so, they are bit stuffed to matchthe longest packet length. Indeed, the source coding and packetizationscheme can be designed to generate packets with equal or similar size,as described in co-pending U.S. patent application Ser. No. 09/668,243entitled “Radio Link Protocol/Point-to-Point Protocol Design forWireless Multimedia Packet Networks that Passes Corrupted Data and ErrorLocation Information Among OSI Layers,” (Attorney Docket Number Lu 7-1),incorporated by reference above. The channel encoder at the applicationlayer takes one data unit from each packet and generates (n−k) parityunits to construct (n−k) additional packets in a vertical packet coding(VPC) structure, shown in FIG. 5A.

The VPC scheme provides transparent Internet-to-Wireless communications.In this case, the transmitter at the Internet multimedia database 105 isunaware of the wireless network 200 further downstream, and performs thesame coding scheme to support packet flows over the Internet or awireless network. On the other hand, for a Wireless-to-Internet packetflow, the gateway 115 between these two networks should embed the frameerror information in the packet, and forward it to the receiver. Anotheroption would be for the gateway to perform packet FEC decoding based onthe frame error information. The gateway 115 discards any packet with anunrecoverable frame error without sending it to the Internet 110. Assuch, the UDP protocol within the Internet remains unchanged. However,this action increases both computational complexity and transmissiondelay at the gateway 115.

Another advantage of the CUDP with VPC of the present invention is thateven if the decoder fails, part of the erroneous packets can still berecovered. Using the scenario in FIG. 5A, packet 1, 2, 4, 5, 6 aredeclared lost if only the packet CRC check is used to validate the data.A (7,4) MDS code can only recover three (3) erasures (7 minus 4).Therefore, without the frame error information, the conventional decoderwill fail. If the frame error information is available, the erasures atcolumns 0, 1, 2, 4, 5, 6 are recovered. Only the column corresponding toframe 3 contains erasure. For compressed multimedia data, this is moreimportant since more information means better error concealment andrecovery. If using a UDP Lite protocol, on the other hand, a (7,4) MDScode can recover one error and one erasure, or three erasures; thereforeit can only recover columns 0, 4, 5 and 6.

Long Vertical Packet Coding (LVPC) Scheme

(n, k) MDS codes achieve better error/erasure correction efficiency as nincreases, for the same redundancy ratio (n−k)/n. The FEC encoder 400can increase n by coding L multiple columns of data units together. Thisgenerates X/L coded streams, each corresponding to a (nL, kL) MDS codes.This coding scheme is referred to as long vertical packet coding (LVPC),shown in FIG. 5B.

Using the scenario shown in FIG. 5B, and assuming L=m=7, the dimensionof the MDS code is (49,28) which can recover 21 erasures. From FIG. 5B,the channel error and congestion yields 19 erasures that can all berecovered. LVPC achieves higher efficiency compared to VPC. However, ifthe decoder fails in LVPC, all the erasures can not be recovered, whilein VPC, part of the erasures can be recovered. In addition, compared toVPC, LVPC has a disadvantage of increased computational complexity forthe IP-only case since it requires the wireless frame size information,which may not be available at the transmitter.

Horizontal/Vertical Packet Coding (HVPC) Scheme

In a further variation, FEC coding is applied to code the wirelessframes in a single packet. As such, the encoder 400 applies verticalpacket coding across the packets, and then applies an outer horizontalcoding scheme within each packet. Similarly, the decoder first performshorizontal decoding to recover frame errors within the same packets, andthen performs vertical decoding. The horizontal packet coding requiresknowledge of the frame size.

It is to be understood that the embodiments and variations shown anddescribed herein are merely illustrative of the principles of thisinvention and that various modifications may be implemented by thoseskilled in the art without departing from the scope and spirit of theinvention.

1. A method for transmitting a multimedia packet from a wireless packetnetwork to a wired network conforming to the Internet Protocol (IP),said multimedia packets encoded using a forward error correction (FEC)coding technique, said method comprising the steps of: embedding frameerror information in said multimedia packet; forwarding said multimediapacket to a receiver on said wired network; and discarding a multimediapacket having an unrecoverable frame error.
 2. The method of claim 1,wherein said forward error correction coding technique employs MaximalDistance Separable codes that are applied to a number, k, of informationpackets comprised of X data units, and wherein up to X codewords areformed of length n using one data unit from each of said k informationpackets.
 3. The method of claim 1, wherein said forward error correctioncoding technique employs Maximal Distance Separable codes that areapplied to a number, k, of information packets comprised of X dataunits, and wherein up to X/L codewords of length nL are formed using Ldata units from each of said k information packets.
 4. The method ofclaim 1, wherein said forward error correction coding technique employsMaximal Distance Separable (MDS) codes that are applied to each of saidinformation packets comprised of X data units to create k informationpackets comprised of X′ data units, and a second set of said MDS codesare applied to of said information packets comprised of X′ data units,and wherein up to X′ codewords are formed using one data unit from eachof said k information packets.
 5. A method for transmitting a multimediapacket from a wireless packet network to a wired network conforming tothe Internet Protocol (IP), said multimedia packets encoded using aforward error correction (FEC) coding technique, said method comprisingthe steps of: decoding said multimedia packet using frame errorinformation; forwarding said multimedia packet to a receiver on saidwired network; and discarding a multimedia packet having anunrecoverable frame error.
 6. The method of claim 5, wherein saidforward error correction coding technique employs Maximal DistanceSeparable codes that are applied to a number, k, of information packetscomprised of X data units, and wherein up to X codewords are formed oflength n using one data unit from each of said k information packets. 7.The method of claim 5, wherein said forward error correction codingtechnique employs Maximal Distance Separable codes that are applied to anumber, k, of information packets comprised of X data units, and whereinup to X/L codewords of length nL are formed using L data units from eachof said k information packets.
 8. The method of claim 5, wherein saidforward error correction (FEC) coding technique employs Maximal DistanceSeparable (MDS) codes that are applied to each of said informationpackets comprised of X data units to create k information packetscomprised of X′ data units, and a second set of said MDS codes areapplied to of said information packets comprised of X′ data units, andwherein up to X′ codewords are formed using one data unit from each ofsaid k information packets.
 9. A system for transmitting a multimediapacket from a wireless packet network to a wired network conforming tothe Internet Protocol (IP), said multimedia packets encoded using aforward error correction (FEC) coding technique, comprising: a memoryfor storing computer readable code; and a processor operatively coupledto said memory, said processor configured to: embed frame errorinformation in said multimedia packet; forward said multimedia packet toa receiver on said wired network; and discard a multimedia packet havingan unrecoverable frame error.
 10. The system of claim 9, wherein saidforward error correction coding technique employs Maximal DistanceSeparable codes that are applied to a number, k, of information packetscomprised of X data units, and wherein up to X codewords are formed oflength n using one data unit from each of said k information packets.11. The system of claim 9, wherein said forward error correction codingtechnique employs Maximal Distance Separable codes that are applied to anumber, k, of information packets comprised of X data units, and whereinup to X/L codewords of length nL are formed using L data units from eachof said k information packets.
 12. The system of claim 9, wherein saidforward error correction coding technique employs Maximal DistanceSeparable (MDS) codes that are applied to each of said informationpackets comprised of X data units to create k information packetscomprised of X′ data units, and a second set of said MDS codes areapplied to of said information packets comprised of X′ data units, andwherein up to X′ codewords are formed using one data unit from each ofsaid k information packets.
 13. A system for transmitting a multimediapacket from a wireless packet network to a wired network conforming tothe Internet Protocol (IP), said multimedia packets encoded using aforward error correction (FEC) coding technique, comprising: a memoryfor storing computer readable code; and a processor operatively coupledto said memory, said processor configured to: decode said multimediapacket using frame error information; forward said multimedia packet toa receiver on said wired network; and discard a multimedia packet havingan unrecoverable frame error.
 14. The system of claim 13, wherein saidforward error correction coding technique employs Maximal DistanceSeparable codes that are applied to a number, k, of information packetscomprised of X data units, and wherein up to X codewords are formed oflength n using one data unit from each of said k information packets.15. The system of claim 13, wherein said forward error correction codingtechnique employs Maximal Distance Separable codes that are applied to anumber, k, of information packets comprised of X data units, and whereinup to X/L codewords of length nL are formed using L data units from eachof said k information packets.
 16. The system of claim 13, wherein saidforward error correction coding technique employs Maximal DistanceSeparable (MDS) codes that are applied to each of said informationpackets comprised of X data units to create k information packetscomprised of X′ data units, and a second set of said MDS codes areapplied to of said information packets comprised of X′ data units, andwherein up to X′ codewords are formed using one data unit from each ofsaid k information packets.